Prevalence and mechanisms of antibiotic resistance in oral bacteria

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Periodontitis occurs in 15% of adults with teeth. Antibiotics are used as an adjunct to standard mechanical therapy for the treatment of periodontitis. As antibiotic use has increased, many bacteria have acquired resistance mechanisms. In the work presented here, the prevalence of antibiotic resistance was determined for periodontal pathogens and commensal species using minimum inhibitory concentration (MIC) assays, DNA probes, polymerase chain reaction, and mating experiments to determine the mobility determinants. The organisms studied included Actinobacillus actinomycetemcomitans, Campylobacter rectus, Treponema denticola, Neisseria perflava/sicca, Neisseria mucosa and Neisseria flava. Tetracycline resistance was found in A. actinomycetemcomitans, T. denticola, N. perflava/sicca, N. mucosa and N. flava. The tetracycline resistance in A. actinomycetemcomitans and T. denticola was due to the presence of the Tet B determinant. The Tet B determinant was found to be mobile in A. actinomycetemcomitans and appears to be associated with a conjugative plasmid. The Tet B determinant was not mobile in the T. denticola isolates examined and was located on the chromosome. The Tet M determinant was present in Neisseria perflava/sicca, and Neisseria mucosa but not in Neisseria flava.Macrolide resistance was found in A. actinomycetemcomitans, C. rectus and commensal Neisseria species. These macrolide resistant species carried a variety of rRNA methylase determinants. The most common determinants found were Erm B and Erm C. The rRNA methylase determinants were located on the chromosome and were mobile in all the species examined.This research establishes that previously described antibiotic resistance determinants originally found in other human pathogens are also present in periodontal pathogens and oral commensal species.